Preparing Trees for Winter

This drought-ravaged summer was extremely hard on trees, said a University of Illinois horticulture educator.

"Trees have been suffering all summer long from drought stress and extreme heat, so it's particularly important this year that we prepare them for winter," said Candice Miller.

Evergreens are a particular source of concern. They are prone to desiccation, or drying out, from the wind or sun. They should be watered well until the ground freezes.

"Evergreens do not drop their leaves like deciduous trees, so they are still living and breathing throughout the winter and need to be able to take up water," Miller said.

Shrubs in very exposed sites may benefit from additional watering and protection. Options include loosely wrapping with burlap, putting up a snow fence or other type of windbreak, or using commercially available anti-transpirants, which are wax-like materials sprayed on plants late in the fall to help prevent them from drying out. These work especially well on broadleaf evergreens.

"Another winter problem plaguing trees is sunscald," noted Miller.

Sunscald occurs when sunlight heats up the south and southwest side of deciduous tree trunks, causing cells to come out of dormancy and become active. If the temperature drops below freezing after sunset or as the weather changes, the active cells are killed, causing injury that may appear later as sunken and discolored bark. Frost cracking can also occur when the trunk warms up and then freezes.

Sunscald can be managed by using commercial tree wraps, which are made of crepe paper and help to insulate the bark. In late October or early November, wrap the trunks upward from the base of the tree to a point just above the lowest branches. This is typically done on younger trees until they are able to develop thicker bark to serve as protection. These trunk guards should be a light color so that they can reflect sunlight during winter, thereby preventing the bark from warming. Be sure to remove tree wrap and tape the following April to avoid girdling and insect damage.

"Winter feeding by rabbits and voles may also be of concern," Miller noted. "Putting up a barrier such as chicken wire or hardware cloth is really the easiest and best defense for trees."

Put a fence around shrubs and put a loose cylinder of hardware cloth around the trunk base of younger trees susceptible to vole or rabbit gnawing. Removing excess vegetation and debris near plants will also help reduce cover, especially for voles.

"Preparing your trees for winter may be a small amount of extra work, but the payoff of having a healthy tree next spring is definitely worth it," Miller concluded.